1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile using an electrophotographic method or an electrostatic recording method.
2. Description of the Related Art
Conventionally, for example, an image forming apparatus using an electrophotographic method employs a process cartridge method for integrating an electrophotographic photosensitive member (a photosensitive member) and process units acting on the electrophotographic photosensitive member into a cartridge, and making the cartridge attachable to and detachable from the main body of the image forming apparatus. The process units include, for example, a charging unit, a development unit, a cleaning unit, a static elimination unit for eliminating static from the photosensitive member, and a toner charging unit for charging transfer residual toner on the photosensitive member.
In the process cartridge method, generally, when a developer stored in a development device serving as the development unit has run out, or when the photosensitive member has come to the end of its life, an operator such as a user or a serviceman replaces the process cartridge, thereby enabling the image forming apparatus to form an image again.
The publication of Japanese Patent Application Laid-Open No. 2006-30963 discusses a technique for detecting whether a process cartridge is correctly attached to a main body of an image forming apparatus. According to the publication of Japanese Patent Application Laid-Open No. 2006-30963, after the process cartridge has been attached to the main body of the image forming apparatus, the image forming apparatus applies a voltage to the process cartridge. Then, if the process cartridge is normally attached to the main body of the image forming apparatus, an electrical contact on the apparatus main body side and an electrical contact on the process cartridge side become electrically connected together, and a current flows between the process cartridge and the apparatus main body. If this current cannot be detected, notification is given that the process cartridge is not attached in a normal position.
There is a process cartridge having a structure where the charging member can be attached to and detached from the process cartridge. In the case of a process cartridge having such a structure, for example, when maintaining the process cartridge, a serviceman may detach the charging member from the process cartridge, clean the charging member, and attach the cleaned charging member to the process cartridge again. In such a case, the charging member may be shifted from the normal position when attached to the process cartridge. In this case, it is possible that a current flows to the charging member. However, the discharge gap between the photosensitive member and the charging member may change in the longitudinal direction of the charging member. This may result in a charging failure.
The technique discussed in the publication of Japanese Patent Application Laid-Open No. 2006-30963 cannot detect the above case even if the process cartridge is attached in the normal position. Further, the act of attaching or detaching the charging member to or from the process cartridge is not frequently performed, but is occasionally performed by an operator such as a serviceman intending to attach or detach the charging member. Even though the charging member has obviously not been attached to or detached from the process cartridge, if the detection is made when the image forming apparatus is turned on or every time an opened door is closed to replace the process cartridge as in the publication of Japanese Patent Application Laid-Open No. 2006-30963, it may take extra time.
Thus, it is necessary to detect the state where a charging member is attached to a process cartridge in a shifted manner, and also to reduce excessive time.